1. Field of the Invention
The invention relates to optical fiber cables. More particularly, the invention relates to plenum-rated optical fiber cables having high modulus buffered optical fibers.
2. Description of the Related Art
Optical energy transmission media such as optical fibers increasingly are being used not only for long haul transmission applications between communications networks but also for local area distribution within individual networks. Accordingly, more and more optical fiber cables are distributed throughout buildings. For example, optical fibers including buffered optical fibers are used in riser cables, which are used to interconnect cables entering building equipment rooms to wiring closets on upper floors. Also, buffered optical fibers are used in plenum space that extends from the riser closets on the floor to satellite closets.
In commercial buildings, the space between a finished (or drop) ceiling and the structure from which it is suspended often is used as a return-air plenum for the building heating and cooling systems. Also, the space conveniently is used for housing communication cables distributed throughout the building. However, because of fire hazards, such cables typically must satisfy various safety requirements to reduce the possibility of fire spreading through the plenum along the cables. Typically, the cables must be tested and approved by an authority such as the Underwriters"" Laboratories. For example, the cables must pass the fire test known as UL910 (also known as the Steiner Tunnel test). Cables meeting such approval are said to be plenum rated.
Although many conventional optical fiber cables are plenum-rated, most of them exhibit shortcomings in other areas. For example, many conventional plenum-rated buffered optical fibers and optical fiber cables have poor optical or mechanical properties. For example, many conventional plenum-rated optical fibers do not have suitable mechanical strength to prevent unacceptable levels of microbending loss in during optical transmission. The mechanical strength of an optical fiber or optical fiber cable is characterized in terms of its modulus or modulus of elasticity, which refers to the relative stiffness or softness of a material. Besides unsatisfactory mechanical properties, many conventional plenum-rated optical fibers are difficult to strip away a portion thereof and thus are ill suited for terminating to various standardized connectors, such as the LC(copyright) connector or the ST(copyright) connector.
Accordingly, it is desirable to have available a high modulus buffered optical fiber or optical fiber cable apparatus that is plenum-rated.
The invention is embodied in an optical fiber minicord cable apparatus and a communication system employing the minicord cable apparatus. The system includes a source of optical energy, an optical fiber minicord cable coupled to the source for transmitting optical energy from the source, and an optical receiver or detector coupled to the minicord cable for receiving optical energy from the source. The optical fiber minicord cable includes a buffered optical fiber having a first strength layer formed around the buffered optical fiber, a first fire resistant jacket formed around the first strength layer, a second strength layer formed around the first fire resistant jacket, and a second fire resistant jacket formed around the second strength layer. The first and/or second fire resistant jackets are made of a fluoropolymer such as poly(vinylidene fluoride) (PVDF) or poly(vinyl chloride) (PVC). For example, fluoropolymers such as PVDF Solef(copyright) 32008 and low smoke poly(vinyl chloride) (LSPVC) Apex(copyright) 910 are useful materials for the fire resistant jackets. The first and/or second strength layers are made of, e.g., polyaramid yarns such as Kevlar(copyright) and Nomex(copyright). The buffered optical fibers, which have a conventional or other suitable structure, comprise a core region, a cladding region formed around the core region, a coating region formed on the cladding region and a buffer region formed on the coating region. The buffer region is made of a material such as nylon (e.g., Huls 1670 Nylon), polyolefin, poly(vinylidene fluoride) (PVDF), poly(vinyl chloride) (PVC), or polyester.
Alternatively, embodiments of the invention include a method of making a high modulus, plenum-rated buffered optical fiber minicord cable. The method includes the steps of providing a buffered optical fiber, forming a first strength layer around the buffered optical fiber, forming a first fire resistant jacket around the first strength layer, forming a second strength layer around the first fire resistant jacket, and forming a second fire resistant jacket around the second strength layer. The buffered optical fiber typically has a conventional arrangement comprising a core region, a cladding region, a coating region and a buffer region. The buffer region is made of a suitable material such as nylon (e.g., Huls 1670 Nylon), polyolefin, poly(vinylidene fluoride) (PVDF), poly(vinyl chloride) (PVC), or polyester. The strength layers are made of, e.g., polyaramid yarns such as Kevlar and Nomex. The first and second fire resistant jackets are made of a fluoropolymer such as poly(vinylidene fluoride) (PVDF) or poly(vinyl chloride) (PVC), including, e.g., PVDF Solef(copyright) 32008 and low smoke poly(vinyl chloride) (LSPVC) Apex(copyright) 910.